What is hydrogen?
Hydrogen is a chemical element represented with the symbol H on the periodic table and atomic number 1. Hydrogen typically exists in molecular form (H2) and is a nontoxic gas at room temperature and pressure but can be condensed to a liquid form at very low temperatures (-423°F or -253°C). Elemental hydrogen is found in compounds like water (H2 O), ammonia (NH3), and hydrocarbons such as natural gas, coal, and oil. Hydrogen occurs naturally on earth only in compound form with other elements in liquids, gases, or solids. Hydrogen combined with oxygen is water (H2O). Hydrogen combined with carbon forms different compounds—or hydrocarbons—found in natural gas, coal, and petroleum. See NREL
Is hydrogen an energy carrier?
Yes, because hydrogen must be produced from other energy sources, it is considered an energy carrier rather than an energy source. Once produced, hydrogen can then be stored, transported, and later used in applications such as hydrogen fuel cells, ammonia production, biofuels, industrial metalworking and welding, and other applications. See NREL
Why are there different colors of hydrogen?
The colors are used to differentiate how the hydrogen was produced. However, it is preferable to classify hydrogen based on the carbon emission intensity of the full production cycle for different production methods (e.g., high-carbon or low-carbon hydrogen). The production of renewable hydrogen — which involves splitting water molecules with electricity — has no or low CO2 emissions if that electricity comes from a dedicated renewables array or a renewables-powered grid. It is important to note that hydrogen’s carbon footprint is not zero if the electricity comes from a fossil-powered grid. Low carbon “blue” hydrogen is produced from natural gas while capturing CO2. Clean hydrogen includes both categories.
How is hydrogen produced?
To produce hydrogen, it must be separated from the other elements in the molecules where it occurs. There are many different sources of hydrogen and ways for producing it for use as a fuel. The two most common methods for producing hydrogen are steam reforming and electrolysis.
- Steam reforming is the most used method of hydrogen production. Commercial hydrogen producers and petroleum refineries use steam-methane reforming to separate hydrogen atoms from carbon atoms in methane (CH4). The steam reforming process results in carbon dioxide emissions.
- Electrolysis is a process that splits hydrogen from water using an electric current.
What is electrolysis?
This is a process of splitting hydrogen and oxygen from water molecules in a unit called an electrolyzer, which is operated by electricity (and heat, in some technologies). An electrolyzer contains an anode and a cathode that are immersed in an electrolyte. An electric current is applied to the electrolyzer, protons, hydroxide ions or oxygen ions can pass, from anode to cathode, depending on the electrolyzer type. These regenerate into hydrogen and oxygen molecules. Today, there are three primary electrolysis technologies: alkaline electrolysis, proton exchange membrane (PEM) electrolysis, and solid oxide electrolysis cells. See NREL
How much water is used to produce hydrogen?
Green hydrogen production uses a theoretical minimum of 9 liters of water for every kilogram of hydrogen created. Given losses in desalination the actual amount is closer to 15 l for every kilogram. In contrast, for every equivalent amount of energy produced, “blue” hydrogen from natural gas-based steam methane reforming consumes approximately 22 liters, and unconventional gas production (hydraulic fracturing) consumes 1.6 to 4.5 liters. See RMI and DOE. Water use can pose a problem in arid locations. Hydrogen projects in such locations are therefore often combined with desalination.
In fact, industry players and governments are looking at large-scale projects to produce water at a scale and cost that can reduce regional water scarcity and enable new water-intensive activities in desert regions of Saudi Arabia, Australia, Chile, and Namibia. Desalinization contributes less than 2 percent of the total capital requirements of green hydrogen and less than 1 percent of the energy requirements.
Is it safe to use hydrogen?
Hydrogen has been safely produced and used in industry for over a century. Like any other fuel, such as gasoline, diesel, or natural gas, hydrogen must be handled appropriately. The systems in use today have been engineered to reduce risk and enable the safe handling and use of hydrogen. Hydrogen derivatives such as ammonia and methanol have their own established safety regimes. See DOE
What is the hydrogen economy?
The hydrogen economy is the vision of an energy infrastructure where clean hydrogen replaces other carbon-intensive fuels and feedstocks such as fossil fuels. The hydrogen economy is intended to complement electrification efforts by targeting hard-to-decarbonize end uses and it also supports a renewables-based electric grid. See DOE.